Conventionally, there are solar cells for solar power generation, such as thin silicon solar cells and CIGS solar cells. (These types of solar cells are collectively referred to as “thin-film solar cells” in the description and claims herein.) Such a thin-film solar cell is formed in the following manner: forming a metal film, or a semiconducting material film such as a silicon film, on one surface of a glass substrate (i.e., deposition or film formation), thereby forming a thin-film layer (having a thickness of several hundred nm to several tens of μm, for example) on the one surface of the glass substrate; and performing patterning on the thin-film layer. Hereinafter, a description is given by taking the substrate of such a thin-film solar cell as one example. (The substrate may hereinafter be simply referred to as a “workpiece”.)
For example, as shown in FIGS. 8A to 8G, a process of manufacturing a thin-film solar cell substrate includes: forming, on the upper surface of a glass substrate 110 (FIG. 8A), a transparent electrode layer (thin-film layer) 111 (FIG. 8B); and performing patterning on the transparent electrode layer 111 by irradiating the transparent electrode layer 111 with a laser beam 115 emitted from a laser machining device, thereby removing part of the transparent electrode layer 111 to form straight machining lines 112A in the transparent electrode layer 111 (FIG. 8C). The substrate 110, including the transparent electrode layer 111 in which the machining lines 112A have been formed, is further processed such that a photoelectric conversion layer (thin-film layer) 113 is formed on the upper surface of the transparent electrode layer 111 (FIG. 8D), and patterning is performed on the photoelectric conversion layer 113 by irradiating the photoelectric conversion layer 113 with the laser beam 115 emitted from the laser machining device, thereby forming machining lines 112B in the photoelectric conversion layer 113 (FIG. 8E). Thereafter, the substrate 110, including the photoelectric conversion layer 113 in which the machining lines 112B have been formed, is further processed such that a back surface electrode layer (thin-film layer) 114 is formed on the upper surface of the photoelectric conversion layer 113 (FIG. 8F). Then, patterning is performed on the back surface electrode layer 114 by irradiating the back surface electrode layer 114 with the laser beam 115 emitted from the laser machining device, thereby forming machining lines 112C in the back surface electrode layer 114 (FIG. 8G). The substrate 110, on which the pattering has been thus performed, is completed as a solar cell module.
FIG. 9 shows a laser machining device 100 of this kind. For example, as shown in FIG. 9, a laser beam 102 (which may hereinafter be simply referred to as a “beam”) emitted from a laser oscillator 101 is split into a plurality of beams of light by a beam splitter 103, and the directions of the respective beams of light are changed by corresponding light-guiding mirrors 104, such that the beams are directed toward a workpiece 106. The focal lengths of the respective beams 102 are adjusted by corresponding beam condensing lenses 105, such that the beams 102 focus on a thin-film layer 107 of the workpiece 106. As a result of the thin-film layer 107 being irradiated with the beams 102, the thin-film layer 107 is partially removed, and thus machining lines 108 are formed.
The above-described patterning by the laser machining device 100 is performed in the following manner: fixing the workpiece 106 on a table of a workpiece feeder 109; feeding the workpiece 106 in an X direction and irradiating the workpiece 106 with the laser beams 102, thereby forming machining lines 108 in the workpiece 106; then feeding the workpiece 106 in a Y-direction by a predetermined amount (corresponding to the pitches of the machining lines); and thereafter, feeding the workpiece 106 in the reverse X direction and irradiating the workpiece 106 with the laser beams 102, thereby forming machining lines 108. By repeating this work, the machining lines 108 are formed in the workpiece 106 sequentially. That is, the work of feeding the workpiece 106 in the X direction and forming the machining lines 108, and the work of feeding the workpiece 106 in the Y-direction, are repeated intermittently.
One example of this kind of conventional technology is as follows: splitting a laser beam emitted from a laser oscillator into a plurality of laser beams by using mirrors; and irradiating a thin-film layer of a solar cell with the laser beams via condensing lenses, thereby forming machining lines (see Patent Literature 1, for example).
In another example of conventional technology, a laser beam whose cross section is in the shape of a thin line is generated by a cylindrical lens, and such laser beams each having the thin-line cross section are emitted in a partially overlapping manner to form a continuous machining mark in the shape of a thin line. In this manner, it is intended to increase the conveyance speed of a substrate, thereby reducing the takt time of the laser machining (see Patent Literature 2, for example).